1. Field of the Invention
The present invention relates to a cartridge case including a tape reel and an upper case and a lower case that enclose the tape reel in a rotatable state, and to an information recording medium including the cartridge case.
2. Description of the Related Art
As one example of an information recording medium that can record a large amount of data, the present applicant has disclosed a single reel-type tape cartridge in Japanese Laid-Open Patent Publication No. 2002-100148. This tape cartridge is constructed of a main case and a single tape reel that is rotatably enclosed inside the main case and around which a magnetic tape is wound. The main case includes an upper case and a lower case that can engage one another. Here, an opening through which a drive shaft of an apparatus (drive apparatus) can pass is formed in the lower case. On the other hand, the tape reel is constructed of an upper flange and a hub in the shape of a bottomed cylinder at whose lower end a lower flange is integrally formed. In this case, ring-shaped engaging teeth (driven teeth), which are caused to engage driving teeth of the drive shaft when the tape reel is rotated, are disposed on a lower surface (outer surface) of the hub.
By investigating the above technology, the present inventor discovered the following problem to be solved. In this tape cartridge, as shown in FIG. 12, an inclined surface 102 is formed on a base part of engaging teeth 101 of a tape reel 100 and a guide surface 112 formed in a complementary shape to the inclined surface 102 is formed at an edge of an opening 111 of the lower case 110. In a state where the tape cartridge is not in use, the inclined surface 102 and the guide surface 112 are in contact so that the tape reel 100 and the lower case 110 are positioned with the center of the tape reel 100 and the center of the opening 111 of the lower case 110 in alignment. During use of the tape cartridge, as shown in FIG. 13, the engaging teeth 101 of the tape reel 100 and the driving teeth (not shown) of the drive shaft engage, the drive shaft presses the tape reel 100 upward and rotates the tape reel 100 in a state where the inclined surface 102 of the tape reel 100 is separated from the guide surface 112 of the lower case 110. The lower case 110 of the tape cartridge is manufactured by injection molding resin. Here, the injection-molded resin shrinks after molding due to its characteristics, and due to such shrinkage, as shown in FIG. 14, there are cases where an edge of the opening 111 of the lower case 110 becomes slightly warped inward (i.e., toward the tape reel 100). Accordingly, during use, sufficient clearance is not maintained in the tape cartridge between the engaging teeth 101 of the tape reel 100 and the edge of the opening 111 of the lower case 110, and as a result, when the tape reel 100 and the lower case 110 become relatively displaced due to vibration or tilting, there is the risk of contact between the engaging teeth 101 of the tape reel 100 and the edge of the opening 111.